Lateral-torsional buckling of prismatic beams with continuous top-flange bracing

Continuous multi-span steel beams are common along the building and highway systems. Typical construction consists of a concrete slab supported by steel beams. The top flange of the beams is typically braced against lateral movement by the metal deck form or by the concrete slab. Design equations for lateral-torsional buckling (LTB) resistance in most specifications ignore the effect of the lateral restraint offered by the metal deck form or by the concrete slab. Finite-element method (FEM) buckling analyses of I-shaped beams were conducted. The beams were subjected to a concentrated load or uniformly distributed load at top flange along with end moments. Traditional moment gradient factors were reviewed and compared with the FEM results. New moment gradient factor for beams with continuous lateral top-flange bracing subjected to a concentrated load was developed using the results of the FEM investigation. The new equation proposed improves current design methods for the LTB problem and increase efficiency in building and bridge design.